The present invention relates generally to the art of microcircuit millimeter wave amplifiers. More particularly, the invention relates to a device (a transverse traveling wave amplifier) for extending the bandwidth of a millimeter-wave wide band amplifier for use in microcircuits. Although the concept appears to be uniquely suited for microelectronics applications and associated fabrication methods it also has features that may offer distinct advantages in conventional classical electronics systems.
In spite of the generally exhilarating advances in solid state miniature technology in recent years, the progress with wide band microwave and millimeter wave amplifiers had always suffered from the natural limitations that are imposed by the physics and material properties of solid state devices. At the same time the temperature sensitivity of the electronics interfaces due to the properties of the constituent materials (Si, GaAs) is viewed as troublesome in future specialized applications.
A basic limitation of customary solid state devices for microwave amplifiers resides with their being a lumped circuit with two or three electrical terminals. As such, they suffer from the conflict between their size and the wavelength of the operational signal. The application of the modern most elegant amplification principle of continuous signal wave field interaction with an energy providing spatially extended electron flow is forestalled because the coherence time/length in solid state electron flows is extremely small, much smaller than a signal period/wavelength so the vital interplay between electron density and electron velocity modulation cannot develop. The lack of opportunity to avail of this interplay restricts solid state technology to a control of the electron flow density by an electrode in a faucet like fashion which necessitates the familiar approach by a three-terminal device and its use in a lumped element circuit. The consequences of this situation manifest themselves in the non-attainability of useful amplifier gain bandwidth performance beyond 50 GHz.
The recent advent of microfabricated gate controlled field emitter devices, although again three (or four) terminal devices, with very appealing physical characteristics, justify hopes for successful penetration of the millimeter wave region beyond 50 GHz. Initially this hope was carried by the extremely short electron transit time in these devices (.about.10.sup.-12 sec.) during which the electron behaves completely ballistic. But application of these very small four-element entities, as a combined network, in a distributed amplifier and its assessment in projective computational designs yields upper frequency limits that lag one to two orders behind a frequency equivalent to the inverse transit time.
The following United States patents are of interest.
U.S. Pat. No. 4,132,956--Russer PA1 U.S. Pat. No. 4,151,476--Jasper, Jr. PA1 U.S. Pat. No. 4,733,195--Tserng PA1 U.S. Pat. No. 4,887,049--Krowne PA1 U.S. Pat. No. 2,708,236--Pierce PA1 U.S. Pat. No. 3,038,100--Harrison PA1 U.S. Pat. No. 3,110,839--Trivelpiece PA1 U.S. Pat. No. 4,967,162--Barnett et al PA1 1. An RF amplifier for electromagnetic signals which comprises: PA1 2. The amplifier of feature 1 wherein the waveguiding structure is an inverted metallic stripline with dielectrically closed sides. PA1 3. The amplifier of feature 1 wherein the waveguiding structure is a metallic waveguide with rectangular cross section. PA1 4. The amplifier of feature 1 wherein the waveguiding structure is a metallic waveguide with elliptical cross section. PA1 5. The amplifier of feature 1 wherein the waveguiding structure is a metallic waveguide with an internal ridge(s). PA1 6. The amplifier of feature 1 wherein the waveguiding structure is a periodic delay line. PA1 7. The amplifier of feature 6 wherein the waveguiding structure consists of two flat identical meander lines vertically offset by the height of the electron interaction space. PA1 8. The amplifier of feature 6 wherein the waveguiding structure consists of two flat identical sets of coupled halfwave length resonator filter elements in longitudinal arrangement along with amplifier direction. PA1 9. The amplifier of feature 6 wherein the waveguiding structure consists of a helical conductor. PA1 10. The amplifier of feature 1 wherein the electron flow originates from a series of field emitter cathodes controlled by a gate electrode(s) and guided by additional electrode(s) prior to entry into the interaction space inside the wave guiding structure. PA1 11. The amplifier of feature 10 wherein the field emitter cathodes are replaced by thermionic cathodes. PA1 12. The amplifier of feature 10 wherein the electron flow originates from a linear succession of individual, or groups of, field emitter cathode tips located along the length of the waveguiding structure. PA1 13. The amplifier of feature 10 wherein the electron flow originates from one or a series of linear wedge type field emitting cathodes located along the length of the waveguiding structure. PA1 14. The amplifier of feature 10 wherein the electron flow originates from a suitably chosen distribution density of field emitting cathodes within the ground plane or below, but within the confines of the projection of the lateral limits of the wave guiding structure.
The patent to Russer teaches a device wherein electromagnetic waves are amplified by traveling through superconductive tunnel layers. The patent to Jasper teaches a device wherein electromagnetic waves are propagated through a serpentine stripline in the presence of a magnetic field. The patent to Tserng teaches a device wherein an electromagnetic wave is applied to a series of interconnected FETs. The patent to Krowne teaches a solid state harmonic amplifier wherein electromagnetic waves are applied by a pair of microstrips to a grating region wherein they cause RF amplification.
Pierce (U.S. Pat. No. 2,708,236) discloses an RF waveguide amplifier. Harrison (U.S. Pat. No. 3,038,100) discloses an RF traveling wave tube amplifier. Trivelpiece (U.S. Pat. No. 3,110,839) discloses an RF traveling wave tube.
Barnett et al (U.S. Pat. No. 4,967,162) describe a novel stripline device which was an extension of a distributed amplifier device published in 1948 (E. L. Ginston, W. R. Hewlett, J. H. Tasberg and J. D. Noe, "Distributed Amplification", Proc. IRE, pp 956-969, August 1948). That publication and the Barnett et al patent rely on the triode principle as means for energy conversion and amplification mechanism. That principle is described by modulation of an electron current emitted from a cathodic electrode by a control electrode generally called gate or grid. After leaving the cathode-gate area, this current modulated electron flow is now capable to deliver power to an external circuit via an anodic electrode. In an extended, distributed or stripline device these above-described electrodes are given a linearly extended shape of transmission lines retaining locally the same operational design features found in the parental designs. The Barnett et al patent confirms that position throughout all of its explanations, specifically so by comments on its figures which clearly distinguish between an RF gate stripline and the other RF stripline(s). Also, the comments on phase velocity point out the necessity of matched propagation of signals since there are separate lines.
A paper by Walter Friz and Morris Ettenberg titled "The Simtron Concept" presented orally at the 3rd International Conference on "Vacuum Micro Electronics", Monterey Calif., July 1990 describes a novel form of a high frequency amplifier which is suitable for realization in a vacuum microelectronics structure. The cathode is a linear array of field emitters or a linear ridge emitter. The rf structure is a Coplanar Waveguide (CPW) which may be fabricated by planar techniques as in solid state devices. The CPW is a TEM transmission line and the interaction may be regarded as an extended triode with spatial variation according to the wavelength. Hence the name SIMTRON - Spatial Injection Modulation of elecTRONs.